Project Information

Abstract:

The invasive brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), has become a significant pest of vegetables in Virginia. Field experiments were conducted on two Virginia farms in 2012 and 2013 to determine if BMSB populations could be maintained below economically-damaging levels in bell peppers through implementation of a trap crop. In 2012, there were no differences in BMSB densities on peppers bordered by a row of trap plants of either sunflower or corn compared to control peppers with no trap border. In 2013, higher numbers of BMSB were observed on control peppers compared to either of the trap crop treatments. There was no effect of trap crop treatment on stink bug damage to pepper fruit in either year. Stink bug damage averaged 30-40% and 20-25% in 2012 and 2013, respectively, regardless of treatment. Also in both years, BMSB egg masses were collected from fields and assessed for parasitism levels from native stink bug egg parasitoids in southwest Virginia to determine the potential biological control impact on this invasive pest. BMSB egg parasitism levels averaged from 6 to 17% across three years of sampling BMSB eggs in trees and on agricultural crops. Additional research studies were conducted to evaluate the efficacy of pyrethroid-incorporated polyethylene mosquito netting as a control tool for protecting vegetables against BMSB and other agricultural pests. Fresh netting as well as netting that had aged in the field for one year were shown to be toxic to BMSB, killing over 70% of nymphs and adults after constant exposure to the screen for 2 hrs. Field efficacy trials showed that the treated screening provided significant control of flea beetles on collards and eggplant and cucumber beetles on melons better than untreated polyethylene screening. Further research should be done on the potential of long-lasting pyrethroid-treated polyethylene screen as a row cover to protect high value commodities from certain insect pests.

Introduction

The brown marmorated stink bug (BMSB), Halyomorpha halys (Stål), a native of eastern Asia was accidently introduced into Pennsylvania in the late 1990’s (Hamilton 2009), and has since spread across much of the continental United States. Isolated populations also exist in Switzerland, France and Canada. Current research and observations in the mid-Atlantic states have shown that BMSB has tremendous potential to reduce yields in numerous agricultural commodities.

Halyomorpha halys can cause significant injury to a wide range of vegetable crops when bugs insert their feeding stylets into plant fruiting bodies, which are often the marketable portion of the crop. In corn (Zea mays), BMSB stylets are inserted through the husk and pierce the tender kernels, which may cause them to become aborted, collapsed, or discolored. Feeding injury to beans (Phaseolus spp.) may result in scarred, faded out sunken areas, and deformed pods. Injury to fleshy fruit, like tomatoes (Solanum lycopersicum L.), and peppers (Capsicum annuum L.), will produce white spongy areas on the skin and tissue damage internally where the feeding stylets were inserted into the fruit. Okra (Abelmoschus esculentus Moench) is also fed upon by this pest resulting in deformed seed pods. Along with reduced quality of the marketable produce, feeding injury to these vegetable may reduce fruit set and subsequent yield by causing adortion of flower buds and young fruiting bodies. In addition to direct damage, the feeding stylets of BMSB also have been shown to transmit pathogenic microorganisms such as bacteria and yeast such as Eremothecium coryli, which can cause fruit rot. Overall losses exceeding 50% due to stink bug damage are common under heavy infestations. Among vegetables, sweet corn, okra and pepper appear to be highly preferred host plants in terms of adult colonization and reproduction. Eggplant (Solanum melongena L.) and green bean are also suitable host plants for egg laying and nymphal development. Tomato appears to be less suitable for BMSB reproduction, but can suffer severe fruit damage, particularly in late August. Other vegetables such as asparagus and those in the cucurbit or brassica groups also may be fed upon by BMSB, but to a lesser degree and dependent upon their proximity to more preferred vegetables.

With the exception of early maturing sweet corn, which may encounter BMSB attack as early as late June, the majority of vegetable crops are attacked from late July to October in the mid-Atlantic U.S (Kuhar et al. 2012). In mixed vegetable plantings, or small farms with diverse crops, there is often significant inter-plot movement of BMSB adults and nymphs over the growing season dependent upon the relative attractiveness of each crop. Stink bug feeding injury on fruit may result in a white spongy area on the surface of the fruit and catfacing damage, which render the fruit unmarketable for fresh market use.

Frequent applications of broad-spectrum insecticides have increased in an attempt to control BMSB. Although several registered insecticides have been shown to be efficacious at controlling BMSB, all of these products also kill beneficial insects, and are therefore, disruptive to IPM systems and not sustainable. This pest poses an an even greater challenge to organic systems, where no real effective control strategies have been identified. Currently available organic pesticides are generally not effective at reducing stink bug populations in field situations (Kamminga et al. 2009). Compared to native stink bug populations, BMSB can occur at unusually high numbers in agricultural systems. These tremendous numbers may be possible in part because there are few natural enemies of BMSB in North America. For instance, about 50% of native stink bug eggs are parasitized (Koppel et al. 2009); while recent reports by Dr. Kim Hoelmer, of the USDA-ARS, indicate that egg parasitism of BMSB may only be around 5%. Additionally, Dr. Hoelmer states that a common obligate parasitoid of native stink bugs, tachinids, are not able to complete development in BMSB (Holtz and Kamminga 2010).

Current control options for BMSB include older broad-spectrum insecticides such as organophosphate, carbamates and pyrethroids that are disruptive and hazardous to the environment. We plan to test cultural, biological, and mechanical control methods that may offer alternative methods of control for BMSB. These methods are part of IPM programs and safer for humans and non-target species.

Stink bugs typically move into an agricultural field from nearby wild hosts; therefore, causing greater injury and crop loss along the perimeter of a field. A potential management method to decrease crop loss is planting a trap crop. Trap crops have been successfully used to reduce stink bugs in soybean by planting more attractive soybeans along the field perimeter (Smith et al. 2009). The stink bugs prefer the early maturing bean pods confining them to an easily treatable area for the grower. Trap crop implementation may reduce chemical sprays since treatment would only be applied to the trap crop instead of the entire field. The reduction in insecticide application saves money for the grower, is safer for the environment, and serves as a refuge for natural enemies.

Our preliminary data from 2010 indicate that BMSB is strongly attracted to sweet corn and sunflower when present on a farm. Thus, sunflower or sweet corn could potentially serve as a trap crop for bell pepper and other high value crops. A successful trap crop may reduce stink bugs in the primary crop and consequently reduce feeding damage. Furthermore, the use of a trap crop offers a habitat for beneficial insects to thrive. Adult egg parasitoids feed on flower nectar. Thus, a trap crop such as sunflower will not only be a refuge, but also a potential food source for beneficial insects.

A mechanical control strategy that has received very little attention in an agricultural system is a physical barrier to prevent insects from feeding on high value plants. A screen barrier such as mosquito netting could eliminate the need for insecticide application. Placed over crop plants, it will protect the high value vegetables from stink bugs as well as other flying pests.

Objective 1: Evaluate the potential of a trap crop of sweet corn and sunflower trap crops to reduce the numbers of BMSB in the primary crop, bell peppers.Objective 2. Evaluate if a trap cropping system increases egg parasitisim of the BMSB.

Objective 3. Evaluating the potential of new technology to reduce stink bug damage on high value vegetables.

Cooperators

Research

Materials and methods:

Obj. 1. To determine if BMSB populations could be maintained below economically-damaging levels in bell peppers through implementation of a trap crop of sunflower or sweet corn, experimental plots were established at three locations in southwest Virginia, Garrett Farms in Glenvar, VA (1 rep), and Kentland Farms near Blacksburg, VA (2 reps). Individual plots were 50 ft by 4 rows. Three replicates were used in 2012 and four replicates in 2013. The control treatment was planted as 4 rows of bell peppers each 20 ft long. Treatments two and three implemented a potential trap crop strategy: one with sunflowers and one with sweet corn. For these treatments, the middle 2 rows of each block consisted of bell peppers while the outer two rows on were comprised of either sunflower or sweet corn.

Stink bug densities were sampled weekly by counting total stink bugs on 10 plants per row (20 plants/plot). On multiple harvest dates, a sample of 25 peppers per row per plot (50 total) were harvested and assessed for stink bug damage several times during the season. If 50 fruit could not be harvested, then all harvested fruit were assessed for damage. Stink bug densities and % stink bug damage to fruit were analyzed using ANOVA and Fisher’s protected LSD to compare means.

Obj. 2. Visual surveys were conducted weekly from May through September on wild hosts (mostly trees bordering farms) as well as agricultural commodities including the pepper experiments described in Objective 1 in western Virginia during the 2011, 2012, and 2013 growing seasons. During the survey, all BMSB egg masses were collected and the number of eggs as well as hatched, unhatched, or parasitized were recorded. Unhatched eggs were brought back to the laboratory and maintained in a growth chamber at 60-80% RH, 27 ± 2°C, and a photoperiod of 16:8 h (L:D) until hatch. Any emerged parasitoids were collected and stored in 70% alcohol. Species identification of parasitoids was confirmed by Christine Diekhoff – USDA-ARS Beneficial Insect Laboratory in Newark, DE. An assessment of BMSB egg parasitism from naturally-occurring species in Virginia was made.

Obj. 3. Efficacy of deltamethrin-incorporated mosquito netting for control of BMSB and other agricultural pests

PermaNet 2.0 (Vestergaard –Frandsen) is a polyethylene bed net that has deltamethrin infused into the plastic, which enables it to be slowly released providing long-lasting (up to five years) control of mosquitoes in order to prevent malaria in developing countries. It may be feasible for these nets to be used during the hot, dry season for alternative ways to help control insect pests in crops. This project was designed to evaluate the efficacy of PermaNet 2.0 at controlling brown marmorated stink bug and other agricultural pests.

Residual toxicity of the screen to BMSB

Beginning in Sept of 2011, baseline efficacy studies were conducted using Permanet 2.0 against brown marmorated stink bug (BMSB) adults and striped cucumber beetle. A 50 ft x 6 ft roll of black and white netting was obtained from Vestergaard-Frandsen (Sweden). The net was cut into 9 cm discs and placed into Petri dishes along with five adult BMSB per dish. Untreated polyethylene screen with similar mesh size was used as a control. Each treatment was replicated five times. The first test was conducted on 13 September. From that date, each screen was placed outside in Blacksburg, VA where it was exposed to ambient conditions. The efficacy bioassay was repeated with aged screen on BMSB adults at 2 weeks, 1 month, and 1 year after exposure (DAE) to the ambient weather.

Field efficacy studies

An experiment was conducted in 2012 at Garrett Farms, Glenvar, VA) using bell peppers. however, the pepper crop suffered heavy disease pressure and no BMSB occurred. Therefore these data are not shown. Additional experiments were conducted to test the concept against various agricultural pests in 2012 and 2013.

In 2012, a series of field experiments were conducted to evaluate the efficacy of Permanet used as a row cover. Each experiment had three treatments including: 1) Permanet screens, 2) untreated screens, and 3) no screens as a control. Each treatment was replicated five times in each experiment. Small portable row cover frames were built using ½ inch diam PVC pipe and were 1.5m long, 0.6m wide and 0.6 m tall. Each experiment used the same set of frames.

Eggplant (variety ‘Black Beauty’) was transplanted on 14 June, 2012 at Virginia Tech’s Kentland Farm near Blacksburg, VA on raised beds with 2-m row centers. Plants were spaced 0.3 m apart. Permanet row covers were placed over five plants per plot on 24 June and the numbers of live flea beetles (Epitrix spp.) on plants per plot was recorded on 25 and 28 Jun.

Muskmelons. ‘Aphrodite’ melons were transplanted at Kentland Farm on 4 June, 2012. The screened frames used for the eggplant experiment were moved from the eggplant and placed over plots of 4 melon plants per plot on 28 June in a completely randomized design. One hour after the screens were placed over the plants; the first evaluation was conducted by counting the number of live and dead cucumber beetles. These counts were conducted again on 29 June, and on 9 July. After which, the melon plants had become too large to continue to use the set up.

Collards. In 2013, the same screens (now 2 years old) were evaluated for controlling flea beetles on collards at Kentland Farms. Collards were direct seeded in mid-May. Plants were approximately 4 inches apart within rows. On 27 May and 10 June, the total number of live crucifer flea beetles (Phyllotreta cruciferae) were recorded from all plants within the plot area of 8 ft2. On 17 June, collards were harvested and fresh weights recorded per plot.

Blueberry. In 2013, the same screens were used in a randomized complete block experiment on blueberries at Garrett Farms. A single bush served as a rep and the experiment had 5 reps. Treatments were applied on June 23, 2013. On July 4 and July 11, the number of BMSB nymphs per blueberry plant were recorded. All data were analyzed using ANOVA and means were separated using Fisher’s LSD.

Research results and discussion:

Obj. 1. In 2012 there was no signicant effect of trap crop treatment on either cumulative numbers of stink bug nymphs over the season on peppers (Fig 1), or stink bug-damaged peppers at harvest (Fig 2). In 2013, fewer stink bugs were observed on peppers bordered by either sunflower or sweet corn (Fig 1); however, there was no effect on % of pepper fruit damaged by BMSB (Fig 2).

Obj. 2. Egg parasitism numbers were recorded for all egg masses (hatched and unhatched eggs) for 2011, 2012, and 2013. In 2011, a total of 2675 BMSB eggs were found with 203 (7.6%) parasitized and successful emergence of 131 parasitoids. In 2012, 3172 eggs were found with 204 (6.4%) eggs parasitized and successful emergence of 38 parasitoids. In 2013, 1210 eggs were found with 203 (16.8%) parasitized. Based on the emergence and identification of 272 parasitoids, the primary species attacking BMSB in Virginia were Anastatus reduvii and several species of Trissolcus including T. euschisti, T. thyanta, T. edessae, T. brochymenae and Telenomus podisi.

Obj. 3. Significantly fewer live flea beetles were counted on eggplants with treated screens compared to no screen or untreated screens (Fig. 1). On melons, significantly more dead cucmber beetles were found on treated screen plots and more live beetles were found on plants with either no screen or untreated screens (Fig. 2). In collards, more live crucifer flea beetles were found on plants with no screens or untreated screens (Fig 3). This correlated with significantly higher yields in the treated screen plots after approximately 3 weeks of treatments being applied (Fig 4). On blueberry bushes, treated screens had fewer BMSB nymphs than bushes with no screen or untreated screens (Fig. 5).

Kuhar, T.P., J. Whalen, and G.P. Dively. 2013. Current status of vegetable pests in the mid-Atlantic U.S. and the impact of brown marmorated stink bug. Entomological Society of America 61st, November 10-13, Austin, TX.

Project Outcomes

Project outcomes:

In areas where the invasive BMSB has become well established, organic growers have suffered the greatest amount of damage to their crops because there are no truly effective solutions for controlling stink bugs. Previous research funded by Southern Region SARE (Mizell 2006, Project No. OS06-029) illustrates the strong potential of using trap crops to manage stink bugs because of their polyphagy and their propensity to move along crop corridors and aggregate on edges of fields. Our attempts to manipulate the behavior of BMSB in a trap crop approach using two preferred host plants, sunflower and corn, were not successful in reducing damage to the cash crop pepper. A different trap crop design employing a potential push-pull strategy where bugs are lured to the trap crop and repelled from the cash crop may have potential for future studies. Use of newly synthesized aggregation pheromones of BMSB might also enhance this pest management strategy in the future.

The approach did not work using the simple experimental design that we used of a single row of sunflowers or sweet corn bordering a strip of peppers. It is possible that a different plot arrangement might have worked better. BMSB have been shown to move from crop to crop presumably as the nutrition of each plant becomes most suitable. Thus, to be effective, a trap cropping approach would need a mix of trap plant species and/or planting dates that mature at different times providing constant optimal food to keep the bugs from moving to the cash crops. Alternatively, a push-pull strategy could be used where bugs are drawn to the trap plants and repelled from the cash crop using chemical repellents or plants.

The survey of egg parasitism of BMSB in Virginia indicated a low level of natural control of this insect, which has likely contributed to the high population levels of this pest in the mid-Atlantic U.S. These data also support the need for classical biological control efforts to increase the levels of biological control of this pest in the U.S. Baseline assessments of BMSB egg parasitism levels in Virginia will be useful to analyze potential changes in parasitism over time.

Our research with deltamethrin-incorporated mosquito netting demonstrates tremendous potential for the use of this product in agricultural pest management. Although this strategy (insecticidal netting) is not currently approved in organic systems, it would reduce insecticide applications directly on food crops, and therefore would be beneficial to the environment. More research is obviously needed, but I believe that our research demonstrated a proof of concept for this control strategy. Row covers (or other exclusion methods) may be the only feasible strategy to protect high value crops from this pest in organic systems.

Economic Analysis

Such analyses were beyond the scope of the project. Because the trap cropping strategy was not effective at controlling BMSB in our experiment, an economic analysis of that would be useless. Long-lasting insecticidal mosquito nets are not commercially available for use in agriculture, and thus an economic analysis of that approach is not feasible. However, crop loss to BMSB can exceed 50% on organic farms in Virginia, and thus, the value of an effective control tactic could be calculated as the reduction in crop losses (x market value).

Farmer Adoption

The grower whose farm that we worked on for this project is very interested in using the insecticidal screens in the future if and when such practices may be approved and a commercial product exists.

Recommendations:

Areas needing additional study

A different trap crop design employing a potential push-pull strategy where bugs are lured to the trap crop and repelled from the cash crop may have potential for future studies. Use of newly synthesized aggregation pheromones of BMSB might also enhance this pest management strategy in the future.

More research into the use of insecticidal screens as row covers for high value crops should be explore because of the level of efficacy demonstrated in our preliminary research.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.

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